Color and infrared filter array patterns to reduce color aliasing

ABSTRACT

Embodiments of a color filter array include a plurality of tiled minimal repeating units, each minimal repeating unit comprising an M×N set of individual filters, and each individual filter in the set having a photoresponse selected from among four different photoresponses. Each minimal repeating unit includes a checkerboard pattern of filters of the first photoresponse, and filters of the second, third, and fourth photoresponses distributed among the checkerboard pattern such that the filters of the second, third, and fourth photoresponses are sequentially symmetric about one or both of a pair of orthogonal axes of the minimal repeating unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 61/841,818, filed 1 Jul. 2013, and U.S.Provisional Application No. 61/856,558, filed 19 Jul. 2013. Bothprovisional applications are currently pending and are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The disclosed embodiments relate generally to image sensors and inparticular, but not exclusively, to color and infrared filter arraypatterns to reduce color aliasing in image sensors, including imagesensors having a global shutter.

BACKGROUND

Color aliasing is a generally undesirable effect caused by certain colorfilter array (CFA) patterns of charge-coupled device (CCD) orcomplementary metal oxide semiconductor (CMOS) image sensors. As atypical example of color aliasing, a small white line on a black orotherwise dark background that registers on individual pixels will beinterpreted as a line containing single pixels of each of the primarycolors registered. It is therefore desirable to design CFA patterns thatminimize color aliasing.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a schematic of an embodiment of an image sensor including acolor filter array.

FIG. 2 is a cross-sectional view of an embodiment of an image sensorpixel including provisions for a global shutter.

FIG. 3 is a cross-sectional view of another embodiment of an imagesensor pixel including provisions for a global shutter.

FIG. 4 is a timing diagram illustrating an embodiment of operation ofthe image sensor pixels of FIGS. 2-3.

FIGS. 5A-5B are cross-sections of a pair of frontside illuminated pixelsand a pair of backside-illuminated pixels.

FIGS. 6A-6F are diagrams that explain the terminology used to describeembodiments of color filter arrays, minimal repeating units, orconstituent filter patterns.

FIGS. 7A-7K are diagrams of embodiments of constituent filter patternsthat can be used to form minimal repeating units.

FIGS. 8A-8F are diagrams of embodiments of minimal repeating units thatcan be formed using one or more of the embodiments of constituent filterpatterns shown in FIGS. 7A-7K.

FIGS. 9A-9F are diagrams of other embodiments of constituent filterpatterns that include infrared filters and can be used to form minimalrepeating units.

FIGS. 10A-10C are diagrams of embodiments of minimal repeating unitsthat can be formed using one or more of the embodiments of constituentfilter patterns shown in FIGS. 9A-9F.

FIGS. 11A-11B are diagrams of embodiments of a low-density infraredconstituent filter pattern and a minimal repeating unit that can beformed using the low-density infrared constituent filter pattern.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Embodiments are described of an apparatus, system and method for colorand infrared color filter array patterns to reduce color aliasing.Specific details are described to provide a thorough understanding ofthe embodiments, but one skilled in the relevant art will recognize thatthe invention can be practiced without one or more of the describeddetails, or with other methods, components, materials, etc. In someinstances, well-known structures, materials, or operations are not shownor described in detail but are nonetheless encompassed within the scopeof the invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one described embodiment. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” do not necessarily all referto the same embodiment. Furthermore, the described features, structures,or characteristics can be combined in any suitable manner in one or moreembodiments.

FIG. 1 illustrates an embodiment of a complementary metal oxidesemiconductor (CMOS) image sensor 100 including a color pixel array 105,readout circuitry 170 coupled to the pixel array, function logic 115coupled to the readout circuitry, and control circuitry 120 coupled tothe pixel array. Color pixel array 105 is a two-dimensional (“2D”) arrayof individual imaging sensors or pixels (e.g., pixels P1, P2 . . . , Pn)having X pixel columns and Y pixel rows. Color pixel array 105 can beimplemented in a frontside-illuminated image sensor, as shown in FIG.5A, or as a backside-illuminated image sensor, as shown in FIG. 5B. Asillustrated, each pixel in the array is arranged into a row (e.g., rowsR1 to Ry) and a column (e.g., column C1 to Cx) to acquire image data ofa person, place, or object, which can then be used to render a 2D imageof the person, place, or object. Color pixel array 105 assigns color toeach pixel using a color filter array (“CFA”) coupled to the pixelarray, as further discussed below in connection with the disclosedembodiments of color filter arrays.

After each pixel in pixel array 105 has acquired its image data or imagecharge, the image data is read out by readout circuitry 170 andtransferred to function logic 115 for storage, additional processing,etc. Readout circuitry 170 can include amplification circuitry,analog-to-digital (“ADC”) conversion circuitry, or other circuits.Function logic 115 can store the image data and/or manipulate the imagedata by applying post-image effects (e.g., crop, rotate, remove red eye,adjust brightness, adjust contrast, or otherwise). Function logic 115can also be used in one embodiment to process the image data to correct(i.e., reduce or remove) fixed pattern noise. Control circuitry 120 iscoupled to pixel array 105 to control operational characteristic ofcolor pixel array 105. For example, control circuitry 120 can generate ashutter signal for controlling image acquisition.

FIGS. 2-4 illustrate embodiments of pixels including a global reset orglobal shutter. These embodiments are further described in U.S. Pat. No.7,781,718, which is hereby incorporated by reference in its entirety.The illustrated global-shutter pixels can be used in a pixel arraycoupled to any of the color filter arrays described herein.

FIG. 2 illustrates of a cross-section of a sample “one-shared” pixelstructure having a barrier implant that is implemented in a pixel array.Pixel structure 200 includes a substrate 202 in which P-well structures204 and 206 are formed. Photodiode region 210 is implanted and/ordiffused in substrate 202. Photodiode region 210 can be hydrogenatedamorphous silicon formed on the substrate 202. N-type regions 212, 214,and 216 are formed in P-well 204. A pinning layer 222 can be formedabove region 210 which helps to confine photoelectrons to the region 210until readout time. Region 212 can be a doped P-type or a lightly dopedN-type.

Insulating structure 220 is formed above P-well structure 206.Insulating structures 220 can be formed using processes such as shallowtrench isolation (STI) or local oxidation of silicon (LOCOS). Aninsulating structure 220 using an STI process can be formed by etching avoid within P-well structure 206 and depositing a dielectric material(such as silicon dioxide) within the void. The deposited dielectricmaterial can be planarized using CMP.

A storage gate transistor has a gate 224 in an area that is above andbetween regions 210 and 212. The storage gate (SG) transistor iscontrolled by signal SG (as discussed more fully with respect to FIG.6). The storage gate transistor controls flow of electrons from thephotodiode region 210 to the storage gate 224 when the captured chargeis transferred to the storage gate. The storage gate transistor alsocontrols flow of electrons from the storage gate 224 to the floatingdiffusion 214 when the transfer gate is turned on. The primary chargestorage region is the storage gate 224.

A barrier implant 208 is formed in a region beneath storage gate 224 insubstrate 202. The barrier implant can be formed using a P-type implant.Barrier implant 208 helps reduce image lag by helping to prevent chargethat flows through the channel formed beneath the storage gate 224 (whengate 224 is activated) from flowing backwards into region 210.

A photoshield 230 is provided, for example, above storage gate 224 tohelp define an edge of an aperture through which photons 232 can becaptured. Photoshield 230 also helps to prevent photons 232 fromadversely affecting the stored electrical charge of the pixel afterintegration (the operation of the pixel is discussed more fully belowwith reference to FIG. 6). The photoshield 230 structure can be formedby depositing a metal layer or silicides over the storage gate 224.

A transfer gate transistor is formed using regions 212 and region 214 byforming the gate 226 in a region that is above and between regions 212and 214. The transfer gate (TG) transistor is controlled by signal TG,as discussed more fully with respect to FIG. 4. The transfer gatetransistor controls flow of electrons from the storage gate 224 to thefloating diffusion region 214 when the captured charge is beingtransferred for readout. The transfer gate transistor also controls flowof electrons from the floating diffusion region 214 to the photodioderegion 210 when both the storage gate and the transfer gate are turnedon.

A global reset transistor is formed using region 216 and region 214 byforming the global reset gate 228 in a region that is above and betweenregions 216 and 214. The global reset (GR) transistor is controlled bysignal GR, as discussed more fully with respect to FIG. 4. The globalreset transistor controls flow of electrons from the reset voltage(VRST) region 216 to floating diffusion (FD) region 214 when the pixelis being (globally) reset. If the storage gate 224 and the transfer gateare also turned on, the global reset transistor will reset thephotodiode region 210. The global reset transistor also can be used toimplement a row reset of the FD as part of the readout of pixels withinrows.

FIG. 3 illustrates of a cross-section of a sample “one-shared” pixelstructure 300 having a barrier gate transistor that is implemented in apixel array. Structure 300 includes a substrate 302 in which P-wellstructures 304 and 306 are formed. Photodiode region 310 is implantedand/or diffused in substrate 302. N-type regions 312, 314, and 316 areformed in P-well 304. A pinning layer 322 can be formed above region 310which helps to confine photoelectrons to the region 310 until readouttime.

Insulating structure 320 is formed above P-well structure 306.Insulating structure 320 can be formed using processes such as shallowtrench isolation (STI) or local oxidation of silicon (LOCOS). Aninsulating structure 320 using an STI process can be formed by etching atrench within P-well structure 306 and depositing a dielectric material(such as silicon dioxide) within the trench. The deposited dielectricmaterial can be planarized using CMP.

A barrier gate transistor is formed using regions 310 and region 318 byforming the transistor gate 334 in an area that is above and betweenregions 310 and 318. The barrier gate (BG) transistor is controlled bysignal BG, as discussed more fully with respect to FIG. 4. The barriergate transistor controls flow of electrons from the photodiode region310 to region 318. The barrier transistor helps reduce image lag byoperating in conjunction with the storage gate transistor (discussedbelow) helping to prevent charge that flows through the channel formedbeneath the storage gate 324 (when gate 324 is activated) from flowingbackwards into region 310.

A storage gate transistor is formed using regions 318 and region 312 byforming the transistor gate 324 in an area that is above and betweenregions 318 and 312. The storage gate (SG) transistor is controlled bysignal SG, as discussed more fully with respect to FIG. 4. The storagegate transistor controls flow of electrons from the photodiode region318 to region 312.

Photoshield 330 is provided above storage gate 324 and barrier gate 334to help define an edge of an aperture through which photons 332 can becaptured. Photoshield 330 also helps to prevent photons 332 fromaffecting the stored electrical charge of the pixel after integration. Atransfer gate transistor is formed using regions 312 and region 314 byforming the transfer transistor gate 326 in a region that is above andbetween regions 312 and 314. The transfer gate (TG) transistor iscontrolled by signal TG, as discussed more fully with respect to FIG. 6.The transfer gate transistor controls flow of electrons from the(storage) region 312 to (floating diffusion) region 314 when thecaptured charged is being transferred for later measurement. Thetransfer gate transistor also controls flow of electrons from thefloating diffusion region 314 to region 312 when the pixel is beingglobally reset.

A global reset transistor is formed using region 316 and region 314 byforming the global reset gate 328 in a region that is above and betweenregions 316 and 314. The global reset (GR) transistor is controlled bysignal GR, as discussed more fully with respect to FIG. 4. The globalreset transistor controls flow of electrons from the reset voltage(VRST) region 316 to floating diffusion (FD) region 314 when the pixelis being (globally) reset.

FIG. 4 is a timing diagram illustrating operation of a sample globallyreset pixel array using pixel embodiments such as those shown in FIGS.2-3. At time T0, signals GR (global reset), TG (transfer gate), SG(source gate), BG (barrier gate) are asserted. In some embodiments, allrow-select lines are simultaneously asserted during a global reset timeto reset all pixels at the same time. In some embodiments, the SGtransistor and the TG transistor are activated in response to the GRsignal.

With reference to FIG. 3, transistor gates 334, 324, 326, and 328 areall simultaneously activated. In response, signal VRST (reset voltage)propagates from node 316 across the N-channel formed under the gate 328such that region 314 (floating diffusion) is charged to the VRST voltage(less the threshold voltage of gate 328), or to V_(pin) if thephotodiode is fully depleted. With gates 326 324, and 334 beingactivated, region 310 (a photosensitive region of the pixel photodiode)is pre-charged to the VRST voltage (less the threshold voltage of theintervening gates). In the case that the photodiode is a fullydepletable pinned photodiode, the photodiode is reset to V_(pin) so longas V_(pin)<VRST−V_(threshold). Accordingly, the pixels within the pixelarray can be concurrently reset in accordance with the disclosed globalreset.

In FIG. 4, each pixel in the pixel array undergoes an integration periodat time T 1. During the integration period, the photosensitive portion(region 310) of the pixel photodiode is exposed to incident light 332,which causes electron-hole pairs (charge) to be created and accumulated.The integration period ends at time T2, where the barrier gate andstorage gate are activated. Activation of the barrier gate and samplegate allows the cumulative charge to be transferred from the photodiodeto the storage gate. As shown in the figure, the barrier gate isdeactivated before the storage gate is deactivated to help preventbackflow of the accumulated charge from the storage gate back to thephotodiode. The transfer gate is not activated at this time, whichprevents flow of the charge to the floating diffusion region, whichsubstantially maintains its pre-charged level. The charge transferred tothe storage gate is stored there while the storage gate is on.

At time T3, a row-select line is asserted that prepares all pixelswithin the row of a pixel array to be measured. At time T4, the floatingdiffusion voltage (as buffered by the source-followers) is measured. Attime T5, the transfer gate is turned on, allowing charge to betransferred from the storage gate to the floating diffusion. The storagegate is actively turned off to help by forcing charge out of the storagegate. Because the BG is off, the charge in the storage gate is forced totransfer to the floating diffusion. Using FIG. 3 as an example, signalTG of FIG. 3 is activated because the row-select line RS0 is activated.Thus the accumulated charge from integration (the exposure value) istransferred to the floating diffusion. At time T6, the floatingdiffusion voltage, as buffered by the source-followers, is measured. Atthe end of time T6, row-select line RS0 is deactivated. Thus, in thismanner, charge can be read out in a row-by-row manner.

FIG. 5A illustrates a cross-section of an embodiment offrontside-illuminated (FSI) pixels 500 in a CMOS image sensor, where theFSI pixels 500 use a color filter arrangement such as color filter array501, which can be a color filter array using any of the MRUs describedherein. The front side of FSI pixels 500 is the side of substrate uponwhich the photosensitive area 504 and associated pixel circuitry aredisposed, and over which metal stack 506 for redistributing signals isformed. Metal stack 506 includes metal layers M1 and M2, which arepatterned to create an optical passage through which light incident onthe FSI pixels 500 can reach photosensitive or photodiode (“PD”) regions504. To implement a color image sensor, the front side includes colorfilter arrangement 100, with each of its individual color filters(individual filters 503 and 505 are illustrated in this particular crosssection) disposed under a microlens 506 that aids in focusing incidentlight onto PD region 504.

FIG. 5B illustrates a cross-section of an embodiment ofbackside-illuminated (BSI) pixels 550 in a CMOS image sensor, where theBSI pixels use an embodiment of a color filter array 501, which can be acolor filter array using any of the MRUs described herein. As withpixels 500, the front side of pixels 550 is the side of substrate uponwhich the photosensitive regions 504 and associated pixel circuitry aredisposed, and over which metal stack 506 is formed for redistributingsignals. The backside is the side of the pixels opposite the front side.To implement a color image sensor, the backside includes color filterarray 501, with each of its individual color filters (individual filters503 and 505 are illustrated in this particular cross section) disposedunder a microlens 506. Microlenses 506 aid in focusing incident lightonto photosensitive regions 504. Backside illumination of pixels 550means that the metal interconnect lines in metal stack 506 do notobscure the path between the object being imaged and the photosensitiveregions 504, resulting in greater signal generation by photosensitiveregions.

FIGS. 6A-6F illustrate various concepts and terminology that will beused in the discussion of color filter arrays (CFAs), minimal repeatingunits (MRUs), and constituent patterns that follows. FIG. 6A illustratesan embodiment of a CFA 600. CFA 600 includes a number of individualfilters that substantially corresponds to the number of individualpixels in the pixel array to which the CFA is or will be coupled. Eachindividual filter has a particular photoresponse and is opticallycoupled to a corresponding individual pixel in the pixel array. As aresult, each pixel has a particular color photoresponse selected from aset of photoresponses. A particular photoresponse has high sensitivityto certain portions of the electromagnetic spectrum while simultaneouslyhaving low sensitivity to other portions of the spectrum. Because CFAsassign a separate photoresponse to each pixel by placing a filter overthe pixel, it is common to refer to a pixel as a pixel of thatparticular photoresponse. Hence a pixel can be referred to as a “clearpixel” if it has no filter or is coupled to a clear (i.e., colorless)filter, as a “blue pixel” if it is coupled to a blue filter, as a “greenpixel” if it is coupled to a green filter, or as a “red pixel” if it iscoupled to a red filter, and so on.

The set of color photoresponses selected for use in a sensor usually hasat least three colors but can also include four or more. As used herein,a white or panchromatic photoresponse refers to a photoresponse having awider spectral sensitivity than those spectral sensitivities representedin the selected set of color photoresponses. A panchromaticphotosensitivity can have high sensitivity across the entire visiblespectrum. The term panchromatic pixel will refer to a pixel having apanchromatic photoresponse. Although the panchromatic pixels generallyhave a wider spectral sensitivity than the set of color photoresponses,each panchromatic pixel can have an associated filter. Such filter iseither a neutral density filter or a color filter.

In one embodiment the set of photoresponses can be red, green, blue, andclear or panchromatic (i.e., neutral or colorless). In otherembodiments, CFA 600 can include other photoresponses in addition to, orinstead of, those listed. For instance, other embodiments can includecyan (C), magenta (M), and yellow (Y) filters, clear (i.e., colorless)filters, infrared filters, ultraviolet filters, x-ray filters, etc.Other embodiments can also include a filter array with an MRU thatincludes a greater or lesser number of pixels than illustrated for MRU602.

The individual filters in CFA 600 are grouped into minimal repeatingunits (MRUs) such as MRU 602, and the MRUs are tiled vertically andhorizontally, as indicated by the arrows, to form CFA 600. A minimalrepeating unit is a repeating unit such that no other repeating unit hasfewer individual filters. A given color filter array can include severaldifferent repeating units, but a repeating unit is not a minimalrepeating unit if there is another repeating unit in the array thatincludes fewer individual filters.

FIG. 6B illustrates an embodiment of an MRU 602. MRU 602 is an array ofindividual filters grouped into rows and columns. MRU 602 includes Mcolumns and N rows, with columns measured by index and rows measured byindex j, so that i ranges from 1 to M and j ranges from 1 to N. In theillustrated embodiment MRU 602 is square, meaning that N=M, but in otherembodiments N need not equal M.

MRU 602 can be divided into four quadrants, with first through fourthquadrants numbered I-IV and arranged counterclockwise starting from thetop right: quadrant I in the upper right, quadrant II in the upper left,quadrant III in the lower left, and quadrant IV is the lower right. Asdiscussed below, one way of forming an MRU such as MRU 602 is to arrangemultiple constituent patterns that are smaller than MRU 602 in differentquadrants. MRU 602 also includes a set of axes 1 and 2 that areorthogonal and substantially bisect the MRU: axis 1 divides MRU 602 intotop and bottom halves, while axis 2 divides the MRU into left and righthalves. In other embodiments other sets of axes are possible, and theaxes not need not be orthogonal to each other; for example, in otherembodiments the diagonals of the MRU can form the axes of MRU.

FIG. 6C illustrates the terminology used in this disclosure to describesome aspects of MRUs, in particular their symmetry, asymmetry, oranti-symmetry. The figure shows red (R), green (G), and blue (B) filtersposition on the left and right sides of an axis. Filters on the leftside have subscript 1 (R1, B1, etc.), while filters on the right sidehave subscript 2 (R2, B2, etc.).

Row 604 is both physically and sequentially symmetric about the axis,such that the left and right sides are mirror images of each other aboutthe axis. Row 604 is physically symmetrical because the positions ofeach color relative to the axis are the same: R1 and R2 are the samedistance from the axis (xR1=xR2), B1 and B2 are at the same distancefrom the axis (xB1=xB2), and so on. And the row is also sequentiallysymmetric because the color sequence is symmetric about the axis: movingto the right from the axis, the color sequence is RBG and moving to theleft from the axis the color sequence is also RBG.

Row 606 illustrates an embodiment that is not physically symmetric aboutthe axis but is sequentially symmetric. Row 606 is not physicallysymmetric (i.e., it is physically asymmetric) because the position ofeach color relative to the axis is not the same: R1 and R2 are differentdistances from the axis (xR1≠xR2), blue pixels B1 and B2 are atdifferent distances from the axis (xB1≠xB2), and so on. But although theillustrated embodiment is not physically symmetric, it is nonethelesssequentially symmetric because the color sequence is symmetric about theaxis: moving to the right from the axis the color sequence is RBG, andsimilarly moving to the left from the axis the color sequence is alsoRBG.

Row 608 illustrates an embodiment that is physically and sequentiallyasymmetric—that is, neither sequentially symmetric nor physicallysymmetric about the axis. Row 608 is not physically symmetric becausethe position of each color relative to the axis is not the same: R1 andR2 are different distances from the axis (xR1≠xR2), blue pixels B1 andB2 are at different distances (xB1≠xB2), and so on. Similarly, the rowis sequentially asymmetric because the color sequence is not symmetricabout the axis: moving to the left from the axis, the color sequence isRBG, but moving to the right from the axis the color sequence is BRG.

Row 610 illustrates an embodiment that is physically asymmetric andsequentially anti-symmetric. Row 608 is not physically symmetric becausethe position of each color relative to the axis is not the same: R1 andR2 are different distances from the axis (xR1≠xR2), blue pixels B1 andB2 are at different distances (xB1≠xB2), and so on. Similarly, the rowis sequentially anti-symmetric because the color sequence on one side ofthe axis is the exact opposite of the color sequence on the other sideof the axis: moving to the left from the axis, the color sequence isRBG, but moving to the right from the axis the color sequence is GBR.

FIG. 6D illustrates terminology that is used below to describe thedisclosed 4×4 constituent patterns that can be assembled into an 8×8MRU, but the terminology can also be used to describe constituentpatterns of different dimensions and can be used to describe the MRUsthemselves or the color filter array (CFA) as a whole. A major diagonalruns from upper left to lower right, whereas a minor diagonal runs fromupper right to lower left. The four pixel long diagonal that runs fromtop left to bottom right is known as the major long diagonal. Above themajor long diagonal, the two pixel diagonal that runs from upper left tolower right is known as the upper major short diagonal. Below the majorlong diagonal, the two pixel diagonal that runs from upper left to lowerright is known as the lower major short diagonal. The terminology usedfor minor diagonals would be similar, as shown in the figure. Thisdisclosure discusses only major diagonals, but this is only forillustrative purposes. Embodiments involving minor diagonals arealternative embodiments, so although they are not discussed below, theyshould be considered as part of this disclosure.

FIGS. 6E-6F illustrate embodiments of checkerboard filter patterns. Acheckerboard pattern is one in which alternating filters in the arraythat forms the MRU or the array that forms a constituent pattern havethe same photoresponse, for instance filters having a firstphotoresponse. The first photoresponse used to form the checkerboard canalso be called the checkerboard photoresponse. The checkerboard photoresponse, then, takes up substantially half the individual filters in anMRU In the illustrated embodiment the checkerboard photoresponse iswhite or panchromatic, but in other embodiments the checkerboardphotoresponse can be different, such as green. As explained below theremaining spots in the pattern—those that are not part of thecheckerboard—can be filled with filters of second, third, and fourthphotoresponses that are different from the first or checkerboardphotoresponse.

FIG. 6E illustrates a checkerboard embodiment formed by placing filtershaving the checkerboard photoresponse on even-numbered columns (i even)of odd-numbered rows (j odd), and placing filters having thecheckerboard photoresponse on odd-numbered columns (i odd) ofeven-numbered rows (j even). FIG. 6F illustrates a checkerboardembodiment formed by placing filters having the checkerboardphotoresponse on odd-numbered columns (i odd) of odd-numbered rows (jodd), and placing filters having checkerboard photoresponse oneven-numbered columns (i even) of even-numbered rows (j even).

Basic RGBW Constituent Patterns

FIGS. 7A-7K illustrate embodiments of constituent patterns that can beassembled to form an MRU by using sets of four constituent patternsarranged into the quadrants shown in FIG. 6B. FIGS. 7A-7C illustrate afirst constituent pattern, which will be called constituent pattern I,and some of its variations; FIGS. 7D-7K illustrate a second constituentpattern, which will be called constituent pattern II, and some of itsvariations. The constituent patterns illustrated in FIGS. 7A-7K are 4×4patterns that can be assembled in sets of four to form an 8×8 MRU, butin other embodiments the constituent patterns can be of a size differentthan 4×4. MRU's formed from sets of four of these other constituentpattern embodiments can have a size different than 8×8.

Generally, the constituent patterns illustrated in FIGS. 7A-7K use a setof four photoresponses that include a first photoresponse used for thecheckerboard as well as second, third, and fourth photoresponses usedfor the non-checkerboard filters. In the illustrated embodiment thefirst or checkerboard photoresponse is panchromatic or white (W) and thesecond, third, and fourth photoresponses are selected from among red(R), green (G), and blue (B). Other embodiments can, of course, usedifferent sets of photoresponses. For instance, other embodiments caninclude cyan (C), magenta (M), and yellow (Y) filters, clear (i.e.,colorless) filters, infrared filters, ultraviolet filters, x-rayfilters, etc.

In the illustrated embodiments, the number of non-checkerboardfilters—that is, filters of the second, third, and fourthphotoresponses—is made as close to equal as possible. Exact equality canbe achieved in embodiments where the number of non-checkerboard filtersis evenly divisible by the number of photoresponses to be allocated, butonly approximate equality can be achieved in embodiments where thenumber of non-checkerboard filters is not evenly divisible by the numberof photoresponses to be allocated. In other embodiments, filters of eachof the second, third, and fourth photo responses can vary between 0% and100% of the non-checkerboard filters, as well as any individual numberor sub range therebetween.

FIGS. 7A-7C illustrate constituent pattern I and some of its variations.FIG. 7A illustrates constituent pattern I, which because of its filterarrangement can suffer from color aliasing in the diagonal direction. Ifconstituent pattern I is used alone to construct a larger MRU, the samediagonal color aliasing problem will persist. Some variations of theseconstituent patterns can be helpful to reduce color aliasing.

FIG. 7B illustrates constituent pattern I-1, which is a variation ofconstituent pattern I. Contrasting with constituent pattern I, there aretwo primary modifications: the green (G) pixels are now moved to themajor long diagonal, and the blue (B) pixel couplet BB and the red (R)pixel couplet RR are moved to the major short diagonals. Morespecifically, the BB couplet now occupies the upper major shortdiagonal, and the RR couplet now occupies the lower major shortdiagonal. Alternatives to these modifications can include the reversalof diagonals for the BB and RR couplets, having G pixels occupying onlya portion of the major long diagonal, etc.

FIG. 7C illustrates constituent pattern I-2, which is another variationof constituent pattern I. This pattern is similar to constituent patternI-1, except that couplet BB now occupies the lower major short diagonaland couplet RR now occupies the upper major short diagonal. Alternativesare similar as discussed above.

FIGS. 7D-7K illustrate constituent pattern II and some of itsvariations. FIG. 7D illustrates constituent pattern II which, likeconstituent pattern I, can suffer from color aliasing in the diagonaldirection. If constituent pattern II is used alone to construct a largerMRU, the same diagonal color aliasing problem will persist. Somevariations of these constituent patterns can be helpful to reduce coloraliasing.

FIG. 7E illustrates constituent pattern II-1, which is a variation ofconstituent pattern II. Contrasting with constituent pattern II, thereare two primary modifications: the G pixels are moved to occupy theentire major long diagonal and the BR (or alternatively RB) couplets aremoved to the major short diagonals. Alternatives to these modificationsare similar to those discussed in the disclosure relating to the firstembodiment.

FIG. 7F illustrates constituent pattern II-2, which is another variationof constituent pattern II. This pattern is similar to constituentpattern II-1, except that couplet RB is used instead of couplet BR.Alternatives are similar as discussed above.

RGBW Constituent Patterns with Semi-Randomization

To improve the reduction of color aliasing, the basic RGBW constituentpatterns disclosed above can be further modified according to morecomplicated rules. As in the RGBW constituent patterns disclosed above,the first photoresponse (W in the illustrated embodiments) still forms acheckerboard pattern, but the filters having the second, third, andfourth photoresponses (R, G, and B in these embodiments) are allocatedmore randomly, so that the resulting MRU pattern appears more random butstill follows certain rules. Hence the modification process disclosedfor the embodiments illustrated below is termed semi-randomization. Inother embodiments not illustrated, the second, third, and fourth photoresponses can be allocated completely randomly. An increase ofrandomness in the placement of non-checkerboard photoresponsefilters—that is, filters with the second, third, and fourthphotoresponses—is desirable for reducing color aliasing.

FIG. 7G illustrates constituent pattern II-3, which is a variation ofconstituent pattern II. The major long diagonal of this constituentpattern is a mix of constituent pattern II and constituent pattern II-1or II-2. Along the major long diagonal, instead of alternating BR orbeing all G, the top left is B and the bottom right is R, while the twomiddle pixels are G. The upper and lower major short diagonals are thesame as constituent pattern II-2. Alternatives are similar as discussedabove.

FIG. 7H illustrates constituent pattern II-4, which is another variationof constituent pattern II. This pattern is similar to constituentpattern II-2, except that couplet RB now occupies the two middle pixelsof the major long diagonal. Alternatives are similar as discussed above.

FIG. 7I illustrates constituent pattern II-5, which is another variationof constituent pattern II. Several modifications are made here. First,color order along the major long diagonal is reversed from BR to RB.Second, the upper major short diagonal now includes couplet BG insteadof couplet GG. Third, the lower major short diagonal now includescouplet GR instead of couplet GG. Alternatives are similar as discussedabove.

FIG. 7J illustrates constituent pattern II-6, which is another variationof constituent pattern II. Constituent pattern II-6 is similar toconstituent pattern II-5, except that the upper major short diagonal nowincludes couplet GR instead of couplet GG and the lower major shortdiagonal now includes couplet BG instead of couplet GG. Alternatives aresimilar as discussed above.

FIG. 7K illustrates constituent pattern II-7, which is another variationof constituent pattern II. This pattern is similar to constituentpattern II-6, except that an R filter in the major long diagonal issubstituted with a B filter, such that the color pattern is now RBBBinstead of RBRB. Constituent patterns II-3 through II-7 are onlyexamples of the semi-randomization process. There are more examples thatare not shown in the drawings, but are still part of this disclosure.

First RGBW MRU Embodiment and Alternatives

FIG. 8A illustrates an embodiment of a red-green-blue-white (RGBW) MRUusing constituent patterns I and I-1. Constituent pattern I-1 occupiesthe first and third quadrants, and constituent pattern I occupies thesecond and fourth quadrants. The resulting MRU has non-checkerboardphotoresponses (second, third, and fourth photoresponses) that aresequentially symmetric about axis A2 but sequentially asymmetric aboutaxis A1.

There are several alternatives to the present embodiment. First,quadrant assignment to constituent pattern types can be altered. Forexample, constituent pattern I can occupy the second and fourthquadrant, or the first and second quadrant, and so on, whereasconstituent pattern I-1 occupies the remaining quadrants. Second, thenumber of constituent patterns can also be altered. For example, therecan be three constituent patterns I and one constituent pattern I-1, orvice versa. There can also be only one constituent pattern, such asconstituent pattern I-1. Various permutations of quadrant assignment andconstituent pattern can produce a multitude of alternative embodiments,which are not all illustrated or listed in detail here but arenonetheless part of this disclosure.

Second RGBW MRU Embodiment and Alternatives

FIG. 8B illustrates a second embodiment of an RGBW MRU that usesconstituent patterns II and II-1. Constituent pattern II-1 occupies thefirst and third quadrants, and constituent pattern II occupies thesecond and fourth quadrants. The resulting MRU has non-checkerboardphotoresponses (second, third, and fourth photoresponses) that aresequentially symmetric about both axes A1 and A2. Alternatives to thissecond embodiment of an MRU are similar to those discussed above in thedisclosure relating to the first embodiment.

Third RGBW MRU Embodiment and Alternatives

FIG. 8C illustrates a third embodiment of an RGBW MRU using constituentpatterns II and II-2. Two constituent patterns II and two constituentpatterns II-2 are used to construct the final MRU. Constituent patternII-2 occupies the first and third quadrants and constituent pattern IIoccupies the second and fourth quadrants. The resulting MRU hasnon-checkerboard photoresponses (second, third, and fourthphotoresponses) that are sequentially asymmetric about both axes A1 andA2. Alternatives to this third MRU embodiment are similar to thosediscussed above.

Fourth RGBW MRU Embodiment and Alternatives

FIG. 8D illustrates a fourth embodiment of an RGBW MRU using constituentpatterns I and I-2. Two constituent patterns I and two constituentpatterns I-2 are used: constituent pattern I-2 occupies the first andthird quadrants and constituent pattern I occupies the second and fourthquadrants. The resulting MRU has non-checkerboard photoresponses(second, third, and fourth photoresponses) that are sequentiallyasymmetric about both axes A1 and A2. Alternatives to this fourth MRUembodiment are similar to those discussed above.

Fifth RGBW MRU Embodiment and Alternatives

FIG. 8E illustrates a fifth embodiment of an RGBW MRU using constituentpatterns resulting from semi-randomization, specifically constituentpatterns II-3 and II-7. constituent pattern II-7 occupies the first andthird quadrants, and constituent pattern II-3 occupies the second andfourth quadrants. The resulting MRU has non-checkerboard photoresponses(second, third, and fourth photoresponses) that are sequentiallyasymmetric about both axes A1 and A2. Alternatives to this fifth MRUembodiment are similar to those discussed above.

Sixth RGBW MRU Embodiment and Alternatives

FIG. 8F illustrates a fifth embodiment of an RGBW MRU using constituentpatterns resulting from semi-randomization, specifically constituentpatterns II-3, II-4, II-5 and II-6. Constituent pattern II-5 occupiesthe first quadrant, constituent pattern II-3 the second quadrant,constituent pattern II-6 the third quadrant, and constituent patternII-4 the fourth quadrant. The resulting MRU has non-checkerboardphotoresponses (second, third, and fourth photoresponses) that aresequentially symmetric about both axes A1 and A2. Alternatives to thisfifth MRU embodiment are similar to those discussed above.

RGB-IR Constituent Patterns

To improve reduction of color aliasing while improving the infrared (IR)response of CCD or CMOS image sensors, the RGBW constituent patternsdisclosed in FIGS. 7G-7K can be further modified to include IR filters.The resulting RGB-IR pattern will appear to be random but still followscertain rules. It is noted that a red (R) filter allows both red andinfrared light to pass to its respective light sensitive region (e.g.,photodiode), a green (G) filter allows both green and infrared light topass, and a blue (B) filter allows both blue and infrared light to pass.In some embodiments, an infrared (IR) pixel is covered with acombination of RGB filter material that only allows infrared light topass.

In the described RGB-IR constituent patterns the first (checkerboard)photoresponse is green instead of white and the second, third, andfourth photoresponses are selected from among red, blue, and infrared.Other embodiments can, of course, use different sets of photoresponses.For instance, other embodiments can include cyan (C), magenta (M), andyellow (Y) filters, clear (i.e., colorless) filters, infrared filters,ultraviolet filters, x-ray filters, etc.

FIGS. 9A-9F illustrate embodiments of red-green-blue-infrared (RGB-IR)constituent patterns that can be assembled to form an RGB-IR MRU byusing sets of four arranged into the quadrants shown in FIG. 6B. FIG. 9Aillustrates constituent pattern I-3, which is a variation of constituentpattern I. Contrasting with constituent pattern I, constituent patternI-3 has two primary modifications: the green (G) pixels of constituentpattern I have been replaced with infrared (IR) pixels and the white (W)(also referred to as clear, or panchromatic) pixels are replaced withgreen (G) pixels. An IR-IR couplet occupies both the upper major shortdiagonal and the lower major short diagonal, while the major longdiagonal includes a BB couplet in the upper left corner and an RRcouplet in the lower right corner.

Constituent pattern I-3 in FIG. 9A is only one example of a constituentpattern than can be used to construct an 8×8, or larger, MRU. Any of thepreviously-mentioned constituent patterns can be similarly modified.That is, any of RGBW constituent patterns I, I-1, I-2, II, II-1, II-2,II-3, II-4, II-5, II-6, II-7, and their alternatives, can be modified byfirst replacing the green (G) pixels with infrared (IR) pixels, and thenreplacing the white (W) pixels with green (G) pixels. Put differently,RGBW constituent patterns I, I-1, I-2, II, II-1, II-2, II-3, II-4, II-5,II-6, II-7, and their alternatives, can be modified such that the first(checkerboard) photoresponse is green instead of white and the second,third, and fourth photoresponses are selected from among red, blue, andinfrared. Following are several example constituent patterns andresultant MRUs that implement such modifications.

FIG. 9B illustrates constituent pattern I-4, which is another variationof constituent pattern I. This pattern is similar to constituent patternI-3, except that couplet RR now occupies the upper left corner andcouplet BB now occupies the lower right corner of the major longdiagonal.

FIG. 9C illustrates constituent pattern I-5, which is another variationof constituent pattern I. Constituent pattern I-5 is similar toconstituent pattern I-3, except that the IR pixels are moved to themajor long diagonal, the RR couplet now occupies the upper major shortdiagonal, and the BB couplet now occupies the lower major shortdiagonal.

FIG. 9D illustrates constituent pattern I-6, which is similar toconstituent pattern I-5 except that couplet BB occupies the upper majorshort diagonal and couplet RR occupies the lower major short diagonal.

FIG. 9E illustrates constituent pattern II-8, which is anothermodification of constituent pattern II. Contrasting with constituentpattern II, there are two primary modifications: the green (G) pixels ofconstituent pattern II have been replaced with infrared (IR) pixels andthe white (W) pixels are replaced with green (G) pixels. Morespecifically, an IR-IR couplet now occupies both the upper major shortdiagonal and the lower major short diagonal, while the major longdiagonal includes a BR couplet in the upper left corner and an BRcouplet in the lower right corner.

FIG. 9F illustrates constituent pattern II-9, which is another variationof constituent pattern II. This pattern is similar to constituentpattern II-8, except that the IR pixels are moved to the major longdiagonal, a BR couplet now occupies the upper major short diagonal, andanother BR couplet now occupies the lower major short diagonal.

First RGB-IR MRU Embodiment and Alternatives

FIG. 10A illustrates a first embodiment of a red-green-blue-infrared(RGB-IR) MRU using constituent patterns I-3 through I-6, meaning thatconstituent patterns resulting from semi-randomization are included.Constituent pattern I-5 occupies the first quadrant, constituent patternI-3 the second quadrant, constituent pattern I-6 the third quadrant, andconstituent pattern I-4 the fourth quadrant. The resulting MRU hasnon-checkerboard photoresponses (second, third, and fourthphotoresponses) that are sequentially asymmetric about both axes A1 andA2. Various permutations of quadrant assignment and constituent patternnumber can produce a multitude of alternative embodiments, which are notlisted in details here, but are still considered part of thisdisclosure.

As is apparent, the first RGB-IR MRU embodiment shown in FIG. 10A is amodified version of the fourth RGBW embodiment shown in FIG. 8D. Thatis, the first RGB-IR embodiment can be formed by taking the fourth RGBWMRU embodiment, replacing the green (G) pixels with infrared (IR)pixels, and replacing the white (W) pixels with green (G) pixels.

Second RGB-IR MRU Embodiment and Alternatives

FIG. 10B illustrates a second RGB-IR MRU embodiment using constituentpatterns II-8 and II-9, meaning constituent patterns resulting fromsemi-randomization are included. Constituent pattern II-9 occupies thefirst and third quadrants, while constituent pattern II-8 occupies thesecond and fourth quadrants. The resulting MRU has non-checkerboardphotoresponses (second, third, and fourth photoresponses) that aresequentially asymmetric about both axes A1 and A2. Various permutationsof quadrant assignment and constituent pattern number can produce amultitude of alternative embodiments, which are not listed in detailshere, but are still considered part of this disclosure.

As is apparent, the second RGB-IR MRU embodiment is a modified versionof the second RGBW MRU embodiment shown in FIG. 8B. That is, the secondRGB-IR MRU embodiment can be formed by taking the second RGBW MRUembodiment, replacing the green (G) pixels with infrared (IR) pixels,and replacing the white (W) pixels with green (G) pixels. Any of thepreviously discussed RGBW MRU embodiments can be similarly modified toinclude IR pixels.

Third RGB-IR MRU Embodiment and Alternatives

FIG. 10C illustrates a third RGB-IR MRU embodiment of an infrared MRUusing constituent patterns II-8 and II-9, meaning constituent patternsresulting from semi-randomization are included. Constituent pattern II-9is positioned in the first and third quadrants, while constituentpattern II-8 is positioned in the second and fourth quadrants. Theresulting MRU has non-checkerboard photoresponses (second, third, andfourth photoresponses) that are sequentially symmetric about both axesA1 and A2.

In some embodiments, the constituent patterns and the resultant RGB-IRMRU can be constructed following a first rule of composition thatdictates ratios of green (G), blue (B), red (R), and infrared (IR)pixels. In one embodiment, the first rule of composition can dictatethat a constituent pattern include approximately 50% Green filters,12.5% Blue filters, 12.5% Red filters, and 25% Infrared filters. Thisfilter ratio can be beneficial in certain applications, such as inthree-dimensional (3D) imaging.

As shown above, each of constituent patterns I-3 through I-6, II-8, andII-9, and each of the resultant first and second RGB-IR MRUs followsthis rule. That is, each of the constituent patterns I-3 through I-6,II-8, and II-9 have 50% Green filters, 12.5% Blue filters, 12.5% Redfilters, and 25% Infrared filters. Similarly, both the first and secondRGB-IR MRUs also include 50% Green pixels, 12.5% Blue pixels, 12.5% Redpixels, and 25% Infrared pixels. But in some embodiments the constituentpatterns themselves need not follow the first rule of composition,provided that the resultant RGB-IR MRU does. That is, furtherrandomization of the constituent patterns can be performed as long asthe resultant color and IR filter array pattern still complies with thefirst rule of composition.

Fourth RGB-IR MRU Embodiment and Alternatives

In some embodiments, the constituent patterns and the resultant RGB-IRMRU can be constructed following a second rule of composition thatprovides for a lower density of infrared (IR) pixels. In one embodiment,the second rule of composition can dictate that a pattern includeapproximately 50% Green pixels, 18.75% Blue pixels, 18.75% Red pixels,and 12.5% Infrared pixels. A ratio such as that provided for by thesecond rule of composition can be beneficial in certain applications,such as in night vision imaging.

FIGS. 11A-11B illustrate embodiments of a low-density IR constituentpattern and a corresponding embodiment of an MRU. FIG. 11A illustrates alow-density IR constituent pattern. FIG. 11B illustrates a fourthembodiment of an RGB-IR MRU that uses the low-density IR constituentpattern of FIG. 11A positioned in all four quadrants. The resulting MRUhas non-checkerboard photoresponses (second, third, and fourthphotoresponses) that are sequentially anti-symmetric about both axesAland A2.

The above description of illustrated embodiments of the invention,including what is described in the abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. These modifications can bemade to the invention in light of the above detailed description.

The terms used in the following claims should not be construed to limitthe invention to the specific embodiments disclosed in the specificationand the claims. Rather, the scope of the invention is to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

The invention claimed is:
 1. A color filter array comprising: aplurality of tiled minimal repeating units, each minimal repeating unitcomprising an M×N set of individual filters, and each individual filterin the set having a photoresponse selected from among four differentphotoresponses, wherein each minimal repeating unit includes: acheckerboard pattern of filters of the first photoresponse, wherein acheckerboard pattern is one in which alternating filters in the set havethe same photoresponse, and filters of the second, third, and fourthphotoresponses distributed among the checkerboard pattern such that thefilters of the second, third, and fourth photoresponses are sequentiallysymmetric about one or both of a pair of orthogonal axes of the minimalrepeating unit, wherein sequentially symmetric means that the sequenceof photoresponse types is in the same order when moving away from eitherside of one or both of the pair of orthogonal axes.
 2. The color filterarray of claim 1 wherein the number of filters of any two of the second,third, and fourth photoresponses are substantially equal.
 3. The colorfilter array of claim 1 wherein the first photoresponse is panchromatic(W), the second photoresponse is red (R), the third photoresponse isgreen (G), and the fourth photoresponse is blue (B).
 4. The color filterarray of claim 3 wherein M=N=8 and the minimal repeating unit is: B W GW G W B W W B W G W G W B G W R W R W G W W G W R W R W G G W B W B W GW W G W B W B W G R W G W G W R W W R W G W G W R.


5. The color filter array of claim 3 wherein M=N=8 and the minimalrepeating unit is: B W G W G W B W W R W G W G W R G W B W B W G W W G WR W R W G G W B W B W G W W G W R W R W G B W G W G W B W W R W G W G WR.


6. The color filter array of claim 3 wherein M=N=8 and the minimalrepeating unit is: B W R W R W B W W G W B W B W G R W G W G W R W W B WR W R W B R W G W G W R W W B W R W R W B B W R W R W B W W G W B W B WG.


7. The color filter array of claim 1 wherein the first photoresponse isgreen (G), the second photoresponse is infrared (IR), the thirdphotoresponse is red (R), and the fourth photoresponse is blue (B). 8.The color filter array of claim 7 wherein the minimal repeating unitincludes: approximately 50% green (G) pixels; approximately 12.5% blue(B) pixels; approximately 12.5% red (R) pixels; and approximately 25%infrared (IR) pixels.
 9. The color filter array of claim 7 wherein M=N=8and the minimal repeating unit is: B G IR G IR G B G G R G IR G IR G RIR G B G B G IR G G IR G R G R G IR IR G B G B G IR G G IR G R G R G IRB G IR G IR G B G G R G IR G IR G R.


10. An image sensor comprising: a pixel array including a plurality ofindividual pixels; a color filter array positioned over and opticallycoupled to the pixel array, the color filter array comprising aplurality of tiled minimal repeating units, each minimal repeating unitcomprising an M×N set of individual filters, and each individual filterin the set having a photoresponse selected from among four differentphotoresponses, wherein each minimal repeating unit includes: acheckerboard pattern of filters of the first photoresponse, wherein acheckerboard pattern is one in which alternating filters in the set havethe same photoresponse, and filters of the second, third, and fourthphotoresponses distributed among the checkerboard pattern such that thefilters of the second, third, and fourth photoresponses are sequentiallysymmetric about one or both of a pair of orthogonal axes of the minimalrepeating unit, wherein sequentially symmetric means that the sequenceof photoresponse types is in the same order when moving away from eitherside of one or both of the pair of orthogonal axes; and circuitry andlogic coupled to the pixel array to read out signals from the individualpixels in the pixel array.
 11. The image sensor of claim 10 wherein thecircuitry and logic include a global shutter that can perform a globalreset on the pixel array.
 12. The image sensor of claim 10 wherein thenumber of filters of any two of the second, third, and fourthphotoresponses are substantially equal.
 13. The image sensor of claim 10wherein the first photoresponse is panchromatic (W), the secondphotoresponse is red (R), the third photoresponse is green (G), and thefourth photoresponse is blue (B).
 14. The image sensor of claim 13wherein M=N=8 and the minimal repeating unit is: B W G W G W R W W B W GW G W B G W R W R W G W W G W R W R W G G W B W B W G W W G W B W B W GR W G W G W R W W R W G W G W R.


15. The image sensor of claim 13 wherein M=N=8 and the minimal repeatingunit is: B W G W G W B W W R W G W G W R G W B W B W G W W G W R W R W GG W B W B W G W W G W R W R W G B W G W G W B W W R W G W G W R.


16. The image sensor of claim 13 wherein M=N=8 and the minimal repeatingunit is: B W R W R W B W W G W B W B W G R W G W G W R W W B W R W R W BR W G W G W R W W B W R W R W B B W R W R W B W W G W B W B W G.


17. The image sensor of claim 10 wherein the first photoresponse isgreen (G), the second photoresponse is infrared (IR), the thirdphotoresponse is green (G), and the fourth photoresponse is blue (B).18. The image sensor of claim 17 wherein the minimal repeating unitincludes: approximately 50% green (G) pixels; approximately 12.5% blue(B) pixels; approximately 12.5% red (R) pixels; and approximately 25%infrared (IR) pixels.
 19. The image sensor of claim 17 wherein M=N=8 andthe minimal repeating unit is: B G IR G IR G B G G R G IR G IR G R IR GB G B G IR G G IR G R G R G IR IR G B G B G IR G G IR G R G R G IR B GIR G IR G B G G R G IR G IR G R.